Dolomite is a mixed carbonate of calcium and magnesium, calcium and magnesium carbonates both decompose to produce metal oxides (MgO and CaO). If 4.84g of residue consisting of MgO and CaO remains when 9.66g of dolomite is heated until decomposition is complete, what percentage by mass of the original sample was MgCO3?
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let x mass MgCO3 (molar mass 83.3 g/mol) let y mass CaCO3 ( molar mass 100.1 g/mol) x + y 9.66 .1) mass CO2 evolved 9.66 - 4.84 4.82 g moles CO2 4.82 g / 44 0.110 moles the ratio between MgCO3 and CO2 is 1 : 1; the ratio between CaCO3 and CO2 is 1 : 1 moles of MgCO3 + Moles of CaCO3 moles of CO2 liberated x / 83.3 + y /100.1 0.110 .2) multiply by 8338.33 100.1 x + 83.3 y 917.2 from 1 above x 9.66-y substituting in 2) 100.1 ( 9.66-y) + 83.3 y 917.2 y 2.96 g mass of CaCO3 so mass MgCO3 9.66 - 2.96 6.70 g % MgCO3 6.70 / 9.66 % 69.4 %
